1. Field of the Invention
This invention relates to a lens meter for measuring the refractive characteristic value at each position of a lens to be inspected and displaying an image of a refractive state diagram from the obtained refractive characteristic values.
2. Description of the Prior Art
Conventionally, there has been known a lens meter in which a measurement light beam emitted from a light source is made incident upon a lens to be inspected, an amount in travel of the light beam which has passed through the lens is then detected by a photosensor, arithmetic control means then calculates the refractive characteristics at each position of the lens from the detection result, and the refractive characteristics of the spherical power, the cylindrical power, etc., of the lens are obtained from the calculated refractive characteristics.
In recent years, however, a progressive power lens (varifocal lens), a distance aspherical lens, and the like, have spread widely as an eyeglass lens. Since the refractive characteristics of the spherical power, the cylindrical power, or the like, of the eyeglass lens are not uniform, unlike those of a spherical lens, it has been impossible for the conventional lens meter to simultaneously measure the refractive characteristics in each position of the eyeglass lens (the lens to be inspected).
However, there has been developed a lens meter which is capable of measuring the refractive characteristics of such an eyeglass lens (see Japanese Laid-Open Patent Publication No. Hei 9-33396). This lens meter comprising a light source, a two-dimensionally arranged microlens array used as an optical member for forming many measurement light beams, and a two-dimensional sensor, such as an area CCD (a charge-coupled device), in order of mention, in which a light beam emitted by the light source which has passed through the microlens array is made many measurement light beams, and thereafter the two-dimensional sensor receives many measurement light beams which has passed through the eyeglass lens (the lens to be inspected), and an arithmetic control circuit processes the output (measured data) given by the two-dimensional sensor. Thereby, the lens meter is capable of measuring the power distribution at each position of the surface of the lens in a short time and is capable of being constructed at a less cost because the number of light sources to be required is one and a mechanical driving portion is not required.
In this lens meter, in a case where the refractive characteristics of an eyeglass lens, such as a progressive power lens, are measured, as shown in FIG. 14, the image of equal power distribution lines 62a, 62b, 62i of the spherical power can be displayed, and as shown in FIG. 15, the image of equal power distribution lines (a1, a2, . . . ai), (a1', a2', . . . ai') of the cylindrical power can be displayed.
Conventionally, however, as shown in FIGS. 14 and 15, the image display of the refractive characteristics of the spherical power or the cylindrical power is made separately, and thus the positional relationship or the refractive characteristics of a distance portion, a near portion, a progressive portion, etc., cannot be easily detected.
A progressive power lens is roughly divided into a distance portion, a near portion, a progressive belt portion, and a sideward portion. The distance portion literally represents a part where one's gaze crosses when one has a distance view. This part occupies a wide area in the substantially upper-half part of a lens and the power of the part is uniform. The progressive belt portion represents an area where the power becomes continuously larger from the upper part to the lower part. The near portion represents an area where the power is relatively large and uniform. The sideward portion represents an area where astigmatism is generated because of the configuration of the progressive lens, and the amount of the astigmatism usually becomes larger toward the edge. When an object is viewed through this area, the viewed object looks distorted.
Even though there is used a lens in which the power of the distance portion is equal to the addition power (the difference between the near power and the distance power), a feeling which one has while wearing eyeglasses varies largely with the area of the distance portion, the width or the increase rate of the progressive belt, the area of the near portion, or the like, and thus manufacturers have come up with lenses having various characteristics. Therefore, a manufacturer by which a lens has been produced and a type of the lens can be recognized from the information of the areas, so that a progressive lens according to needs or a lifestyle of a patient can be selected.
However, any clear boundaries between each area do not exactly lie in the strict sense of the word, and thus each position where variations in power exceeds a certain value is displayed as a boundary. For example, in a case where a boundary between the progressive belt portion and the sideward portion is determined, an inside area and an outside area of a line between points where astigmatism generated according to the configuration of the progressiveness exceed a certain value (e.g., 0.25D) are regarded as the progressive belt portion and the sideward portion, respectively.
In a case where the eye of a patient does not have astigmatism, equal cylindrical power lines on which each cylindrical power is equal are shown in FIG. 15 because the cylindrical power is not treated, for example, the lines ai, ai' are regarded as boundary lines between the areas. On the other hand, in a case where the eye does not have astigmatism, the entire surface of the lens has the cylindrical power because the back surface of the lens is usually regarded as a trick surface in order to treat the cylindrical power. In this case, since the astigmatism generated according to the configuration of the progressiveness is added to the treated cylindrical power for the observation in the sideward portion, the astigmatism according to the configuration of the progressiveness is nullified by the treated cylindrical power, especially in a case where the treated astigmatic power is large. In this case, therefore, as mentioned above, even though equal cylindrical power lines are displayed, as shown in FIG. 16, the lines ai, ai' do not correspond to the boundary lines between the areas and a position (the boundary of the sideward portion) from which distortion is recognized cannot be detected. Further, the astigmatic power and the astigmatic axial angle vary with the patient on treatments of the astigmatism, and the number of the combination thereof becomes extremely large. Therefore, a manufacturer cannot place the distribution characteristics in all conditions on a catalogue, and thus the distribution characteristic curves in a case where there are not any astigmatic treatments are usually placed on the catalogue. As a result, in a case where components of the treated cylindrical power are included in a measurement result, it is impossible to compare the measured curves with the distribution characteristic curves shown in the catalogue, so that the manufacturer and the type of the lens becomes difficult to recognize.
Since measured values in the distance portion do not include the astigmatism according to the configuration of the progressiveness differently from those of the sideward portion, the cylindrical power measured in the distance portion shows cylindrical power treated in order to correct the astigmatism of the patient. On the other hand, since the cylindrical power is added to the astigmatism generated according to the configuration of the progressiveness for measurement in the sideward portion, there has been disclosed a method by which the cylindrical power measured in the distance portion in advance is memorized, and then the memorized cylindrical power in the distance portion is subtracted from measured values of the cylindrical power in each position (the progressive belt portion, the near portion, and the sideward portion) below the distance portion.
According to this method, however, subtraction of the values of the cylindrical power is simply taken without axial angles' being considered. The axial angles of principal meridians of the cylindrical power which have been obtained in the measurement of the distance portion, that is, which have been treated in order to correct the astigmatism of the patient, are treated according to the astigmatic axial angles of the patient's eyes, and become uniform over the entire lens surface. In contrast, the axial angles of principal meridians of the astigmatism generated according to the configuration of the progressiveness vary with the part of the lens, and thus do not relate to the treated axial angles in the least. However, values to be obtained in practical measurement correspond to values including both the one cylindrical power and the other cylindrical power added thereto. The relational equations between the powers D', D" to be practically observed are shown in the following. EQU D'=(D.sub.1 +D.sub.2 +R)/2 EQU D"=(D.sub.1 +D.sub.2 -R)/2 EQU R.sup.2 =D.sub.1.sup.2 +D.sub.2.sup.2 +2 D.sub.1 D.sub.2 cos 2 .gamma.
Herein, reference characters D.sub.1, D.sub.2, and .gamma. denote the treated cylindrical power, the cylindrical power generated according to the configuration of the progressiveness, and the angle between the axes of the cylindrical powers, respectively.
Although the cylindrical power C to be practically measured is obtained from C=D'-D", the true value of the cylindrical power according to the configuration of the progressiveness D.sub.2 cannot be obtained if C-D.sub.1 is simply used with the axial angle's being neglected. Therefore, even though the equal cylindrical power lines are displayed according to the values obtained with the axial angle's being neglected, the displayed lines do not correspond to the true lines.